Efficiently converting motion from one form to another is an age-old challenge that is relevant to many areas of technology. One may consider it to be particularly relevant to the drive systems of occupant-propelled vehicles. For example, traditional wheel chairs have been crafted to be propelled by an occupant's rotating a circular rim, by a motor, and by a second person. However, needs of certain users and deficiencies in prior art systems have given rise to lever drive systems that make more efficient use of an occupant's input force than such systems as circular rims. Consequently, a number of attempts have been made to provide an improved means for converting the oscillating motion of a pivoting lever to a rotary motion of a drive wheel of the chair.
Lever drive chairs have been patented with a unidirectional sprocket imparting rotary motion to the driving wheels of a chair by means of a chain. Others have been disclosed with drive systems incorporating relatively complex ratchet housing and gear arrangements. Another drive system taught by the prior art reveals a lever-actuated, rigid brake band means overlying a circumferential edge of a drum that is drivingly coupled to the driving wheels of the chair by a sprocket and chain combination. That drive system permits the selective driving and braking of the chair by a pivoting of the rigid lever actuator.
Notwithstanding the unchallenged usefulness of the foregoing inventions, such occupant-propelled vehicles with their motion conversion assemblies have left a multiplicity of deficiencies in the art. Among them is the fact that the prior art devices often require a relatively large number of parts such as gears, sprockets, chains, and the like that incidentally increases the cost of manufacturing the devices and the likelihood of mechanical malfunction. Furthermore, prior art systems have been known to be excessively heavy. Also, they do not address many biomechanical needs of a user such as the need for allowing a user's arm to follow an optimal path over a full power stroke and the need to accommodate the varying muscular force that a user typically is able to apply. Still further, prior art assemblies either have not permitted a user to shift the propulsion system's gearing or they have made it disadvantageously difficult to do. Additionally, prior art systems have not been truly portable because they employ standard, relatively large wheel chair wheels that cannot easily be released and removed. Yet further, most prior art motion conversion assemblies do not permit an adjustment of the wheel chair seat height, and they restrict the ability of an occupant to transfer into and out of the chair. Further yet, many prior art systems impart a braking of the chair when a user pushes the drive lever to a most-forward position of the power stroke such that a user must consciously limit a push of the lever and unexpected and dangerous braking is possible.
With these things in mind, it becomes clear that there is a need left by the prior art for a motion conversion assembly that is particularly useful with occupant-propelled vehicles that converts motion between reciprocating and rotary forms in an efficient and simple manner while potentially permitting a user to drive, brake, and steer the vehicle by a single means.
There is a further deficiency in the prior art relative to the steering of occupant-propelled vehicles such as wheel chairs. The problem is particularly prevalent with chairs propelled by a single-arm force receiver, such as a drive lever. Steering with such prior art devices has proven mechanically and functionally complex, commonly presenting users with an ergonomically unfriendly steering apparatus. For example, in some devices, a user is required to rotate a control grip about an axis that is generally perpendicular to the user's arm to rotate a caster wheel via a chain, joint, or lever connection. In some steering mechanisms of this type, the grip is longitudinally aligned with its axis of rotation. In others, the grip is perpendicular to its axis of rotation. In both arrangements, many find the required contortion of one's wrist and arm while expending a driving force upon a force-receiving lever difficult and uncomfortable. Furthermore, the steering direction inadvertently may be affected by one's exertion of a propelling force.
Similarly inefficient and uncomfortable are prior art steering devices that require a user to rotate a shovel type handle. Other steering systems include complex multi-gear force transmission arrangements, and prior art systems commonly do not provide a means for disengaging the steering controls to allow free motion of the caster as would be useful when the chair is to be pushed by a second person. In total, one sees that prior art devices are undesirably complex and uncomfortable to operate. Consequently, it would be advantageous if one were to provide a steering arrangement that is simple, effective, and durable while being comfortable to operate.